Both the Grigg's and Cerge's are good options and both have some things that favor one over the other, depending on what we each like or feel we need. The Grigg's is somewhat cheaper to build and can be sized to fit most any tank as long as there is room for the extra height. The Cerge's has the downside of the filter housing being a bit more expensive to buy and takes more width as it is short and fat. But both need a pump to create the water flow to move the water through as the CO2 is dissolved into it. Some form of pump to get the water out of the tank, through the reactor, and back into the tank.